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What is the meaning of dropstones in the rock record?

Figure 1. Outsized clast in rhythmites from the Gowganda Formation,
Ontario, Canada. Rhythmites are considered to be a distal turbidite (Geological
Survey of Canada).

Dropstones are rocks whose diameter is larger (outsized) than the thickness of the
sediment beds within which they are found. Sometimes large ‘rocks’ within
fine-grained, massive sediments are considered dropstones. Dropstones have commonly
been interpreted as being dropped into the sediment by icebergs floating in a lake
or the ocean. This interpretation is considered one of the three main diagnostic
features for ancient ice ages, which occurred hundreds of millions to billions of
years ago within the uniformitarian timescale.1
The ice age interpretation is considered proven, or at least well founded, when
boulders are found within thin beds, especially if those beds are couplets of silt
and clay or sand and silt, assumed to be varvites, the consolidated equivalent of
a varve (figure 1). A varve is a couplet of different sublayers laid down in one
year.

Non-glacial occurrences of dropstones

It is also well known that dropstones can occur as a result of non-glacial mechanisms.2 Dropstones can also end up
on the bottom of a lake or ocean due to sea ice rafting, floating kelp, tree stumps,
swimming animals with stomach stones, sinking projectiles and even waterspouts that
pick up boulders on the beach and carry them over the water.3 Because of the variety of emplacement mechanisms,
dropstones should be equivocal paleoclimatic indicators. They certainly should not
be diagnostic of an ancient ice age.

Although the sediments that contain the dropstones are commonly assumed to have
settled over many years, sometimes these sediments are actually products of mass
flow, and the rocks are actually transported laterally. Many presumed dropstones
in fine-grained sediments have been reinterpreted as stones emplaced laterally by
turbidity currents, a fast-moving, bottom-hugging flow of sediment. One example
is the rocks within thin bands from the famous 2.2 billion-year-old Gowganda Formation,
Ontario, Canada (figure 1). This formation was considered a classic dropstone varvite
until reinterpreted as rocks within a distal turbidite,4 which is the far travelled product of a turbidity
current. Distal turbidites can mimic varves.

There are other reinterpretations of supposed ice age dropstones as emplaced laterally
by mass flow. A Neoproterozoic deposit in Namibia was interpreted as being from
an ice age because of the presence of dropstones in varvites. However, the whole
deposit has been reinterpreted as a product of mass flow.5,6 A
presumed ice age deposit with dropstones in the Canning Basin, Western Australia,
was redefined as the product of subaqueous mass flow.7 The supposed dropstones were likely deposited laterally
in the mass flow.

The meaning of dropstones in ‘tropical settings’

There are of course many occurrences of dropstones that provide no or equivocal
evidence for the environment of emplacement. Such cases are especially evident when
the dropstones are found in presumed tropical settings. There is no choice but to
advocate emplacement was by non-glacial means. It also means that the sediment,
which appears to have been deposited slowly over a long period, was likely deposited
rapidly, probably by a horizontal mass flow mechanism.

Figure 2. Rocks in tree roots, Black Hills, South Dakota.

A number of these dropstones in fine-grained layers are found in Mesozoic sediments
within the uniformitarian geological column. The Mesozoic has been assumed to be
a very warm period on Earth in which there were no ice sheets at high latitudes
and very few if any mountain ice caps.8
Such deductions are especially based on warm climate polar flora and fauna. In spite
of the fossil evidence, some researchers are positing glaciations in Antarctic during
the Mesozoic, maybe to account for what the researchers believe are real ice rafted
dropstones. One recent effort claimed that Antarctica built up an ice sheet, half
the size of the current ice sheet, during a ‘brief’ 200,000-year period
in the supergreenhouse Cretaceous period!9,10

As an example of Mesozoic ‘dropstones’, the origin of 1-m (B-axis) quartzite
boulders found in Cretaceous sandstone in South Australia has been debated for 100
years.11 Because the boulders
are fossiliferous and presumably from the Devonian period, they are believed to
have been transported at least 1,000 km toward the west and northwest. A few of
the boulders are facetted and striated, an assumed sign of glaciation, but which
can be duplicated by mass flow and other processes.12 Although acknowledging the boulders were last
transported by mass flow, the researchers suggest that the boulders were really
transported great distances by the ‘Permian glaciation’ and reworked
by mass flows to the location where they are currently found in Cretaceous sedimentary
rock.

Another example comes from the Jurassic and Cretaceous of northeast Siberia.13 Dispersed rocks within
fine-grained marine sediments with rare warm-temperate plant fossils are attributed
to mass movement.

A recent report from the middle Mesozoic of Spain assumed a tropical lacustrine
setting, but disclosed that dropstones occur in fine-grained limestone.14 Because of the presumed tropical setting and the
lack of presumed glacial features on the rocks, the researchers eliminated iceberg
rafting from an ice sheet. They also discounted mass flow because of the fine-grained
limestone. So, they are left with a hydrodynamic paradox:

‘The occurrence of outsized stones within featureless micrite [fine-grained
limestone] indicative of low-energy conditions involves a hydrodynamic paradox which
can only be resolved by their vertical or oblique emplacement in the host sediment
as dropstones.’15

To solve the paradox, the researchers opted for rafting in the roots of trees. But
they did admit that ice rafting is not a sound glacial criterion:

‘If wood rafting is a possible depositional mechanism, the rafted occurrence
of dropstones is consequently not a sound criterion for inferring the existence
of glacial conditions in lacustrine environments.’15

Dropstone varvites are also reported in tropical Jamaica from the Eocene and Pliocene
within the uniformitarian geological column.16
Isolated boulders up to 1.5 m in diameter were found within thinly bedded turbidites
within the Eocene formation. Two large siltstone boulders were discovered in Pliocene
marlstone, a muddy limestone. Iceberg and sea ice rafting are eliminated. They dismissed
tree rafting because of the lack of fossil wood (in a Flood model such a deduction
would not hold). So, they concluded that the fine-grained or fine-bedded deposit
containing the boulders was deposited by mass flow.

The meaning of dropstones within the Flood

Uniformitarian scientists are sometimes faced with a hydrodynamic paradox because
of the large rocks within what they believe are slowly deposited sediments. But
creationists have more options with rapid sedimentation during the Flood.

We would expect many more true dropstones from the holdfasts of floating kelp, tree
roots (figure 2) ripped up by the Flood, and other ‘high energy’ mechanisms.
Many dropstones would fall from any floating log mat on the floodwater.

Numerous mass flows would have occurred during the Flood, and they should commonly
incorporate ‘dropstones’ emplaced laterally.

Numerous mass flows would have occurred during the Flood, and they should commonly
incorporate ‘dropstones’ emplaced laterally. Sedimentation was extensive
during the Flood and currents would also have been strong at times. We would also
expect to find evidence of large-scale submarine sliding of freshly-deposited sediments.
So, during the Flood, mass flows would likely have been many hundreds of metres
thick, covered tens of thousands of square kilometres, and moved at rapid velocities
for such volumes of sediment. Rocks entrained within such mass flows can be carried
long distances. They can settle within fine-grained sediments, but because the flow
is so thick, the rocks could be deposited before they sank to the bottom of the
flow. Such rocks would end up ‘floating’ in fine-grained sediments or
finely-bedded sedimentary rocks. They would have the appearance of dropstones and
may not have the appearance of a mass flow product. This is probably the case for
the Spanish example above, since the rocks were found dispersed within 8,000 m of
sedimentary rock!17

The gastroliths found in fine-grained sediments from the ‘Lower Cretaceous’
Cloverly Formation have been interpreted as material carried 200 to 400 km in a
mass flow.18,19 This could well be another example of material
deposited in the Flood. Billions of nautiloids (similar to ‘floating rocks’)
were deposited in a 2-m-thick bed at the bottom of the Redwall Formation in the
Grand Canyon and vicinity.20

Dropstones do not seem to be a problem for the Flood paradigm, but are sometimes
a conundrum within the uniformitarian model.

Flint, R.B., Ambrose, G.J. and Campbell, K.S.W., Fossiliferous
Lower Devonian boulders in Cretaceous sediments of the Great Australian Basin, Transactions
of the Royal Society of South Australia104(3):57–65,
1980. Return to text.

Chumakov, N.M. and Frakes, L.A., Mode of origin of dispersed
clasts in Jurassic shales, southern part of the Yana-Kolmya fold belt, North East
Asia, Palaeogeography, Palaeoclimatology, Palaeoecology128:77–85,
1997. Return to text.

Readers’ comments

I saw in road cuts in SE Kentucky what appear to be "drop stones". However, they were the shape of the outside of two saucer plates, one upside down on the other and the rock was sedimentary with small layering, horizontal layering not the same as the matrix rock which also was sedimentary and usually those layers are not as small or thin as the ones in the "drop stone". Some have even been removed and have the shape of fat flying saucers. I was thinking that semiconsolidated sediment deposit was moved with most of it becoming fluidized except these drop stones that were shaped by hydraulics of the flow.

I remember seeing a show on Discovery or History Channel that was claiming that dropstones were proof that the Ice Age was more extensive than thought. I was still new to the creation arguments for the Flood and I saw how illogical it was to assume that the Ice Age was the reason for drop stones. A massive flood could very easily make dropstones.

We recently visited Death Valley in California and I saw one of these drop stones in Marble Canyon. Before I started reading creationist literature I didn’t see many things in nature like drop stones, fossils, cross bedding, etc.

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